[opendtv] Re: The "real" problem with OFDM in the U.S.

From: Tom Barry <trbarry@xxxxxxxxxxx>

To: opendtv@xxxxxxxxxxxxx

Date: Mon, 07 Mar 2005 19:34:21 -0500

Manfredi, Albert E wrote:
> If you want to avoid dead zones, as we must here,
> then adjacent markets won't be able to share
> frequencies. Even with the small stick approach.
> But the next market over can use those frequencies,
> *same as now*.
Is there any topography where someone located equally (at any distance)
between two stations with the same power and channel is not in a dead zone?
- Tom
> Craig Birkmaier wrote:
>
>
>>The coverage criteria was based on the same old
>>story - market-into-market interference. It had
>>almost nothing to do with equaling NTSC coverage,
>>other than the reality that you still have to
>>protect for interference into neighboring markets.
>
>
> Correct. Which means, it had a lot to do with
> coverage, and the constraints are the usual ones:
> preventing interference between adjacent markets.
>
> As always, context matters. So let's ask "as opposed
> to what?"
>
> If there are no clearly defined "guard zones" between
> markets, where no signal is required, then this
> interference issue will *always* emerge. Even with
> small sticks in SFNs.
>
> There are no dead zones between markets up and down
> the East Coast, for example. Less sparsely populated
> areas, sure. But they all belong to at least one
> market, if not two markets.
>
> It would be possible to create coverage, with some
> amount of realism, with smaller, lower power sticks,
> spread reasonably far apart. This requires
> synchronization between towers (that no COFDM
> country has adopted as a solution yet). But okay,
> let's postulate such a scheme. It can be done here
> as well as anywhere.
>
> If you want to avoid dead zones, as we must here,
> then adjacent markets won't be able to share
> frequencies. Even with the small stick approach.
> But the next market over can use those frequencies,
> *same as now*.
>
> An example might be Balt/Wash, Philadelphia, NYC.
> Baltimore and Washington overlap, and must do so.
> Many communities belong to both markets.
>
> The area between the Balt/Wash and Phila markets
> must also be covered completely. No justification
> for creating dead zones. Whether you deploy big
> or small sticks, this means that you can't use
> the same frequencies in Balt/Wash and Philadelphia.
> And many of those communities would belong to
> both Baltimore and Phildelphia markets anyway,
> legitimately, which further makes the point.
>
> So the question is, can the next major market over,
> NYC, use the same frequencies as Balt/Wash?
>
> NYC and Baltimore (and DC) use the same VHF
> frequencies (Channels 2, 4, 5, 7, 11). VHF being
> worst case, this shows that if you want to
> create continuous coverage, big sticks and
> smaller sticks don't make a huge difference in
> terms of frequency planning.
>
> It's coverage area without dead zones that creates
> the problem. We have big markets to cover here,
> and no wilderness areas between them.
>
> I'll agree that a more sharply defined coverage
> contour can reduce interference further away from
> the boundary zones between adjacent markets, But
> where it really *matters*, there is not a big
> difference. And the frequency plans would not
> be dramatically different. And *certainly* not if
> you stick to your idea of three or four towers
> only, per major market. That design wouldn't even
> create a particularly sharp contour.
>
> Bert
>
>
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